In order to meet existing and future particulate emission standards for internal combustion (IC) engines, in particular diesel engines, manufacturers of diesel engines are using particulate filters (PF, also referred to as particulate traps). Such particulate filters are typically placed downstream of the turbocharger turbine and remove solid particulate matter before it exits the exhaust system to the ambient environment. After a particulate filter collects particulates for a period of time, increasing the exhaust temperature to a suitable level (e.g., above a minimum of 600° C.) cleans the filter (also known as regenerating) since the oxygen in the exhaust burns the accumulated carbon in the filter.
Particulate filters for diesel engines are typically relatively large and expensive, and regeneration under light load conditions is problematic because attaining the necessary exhaust temperature is difficult. This high exhaust temperature is typically accomplished by adding fuel to the exhaust of the diesel engine and flowing this mixture through a diesel oxidation catalyst (DOC). However, the mixture temperature entering the DOC has to be a minimum of about 300° C. to ensure good oxidation of the added fuel. Various means of obtaining the necessary 300° C. exhaust temperature at light loads and low ambient temperatures have been proposed and put into production. Methods of increasing exhaust temperature include adding additional load on the engine, retarding injection timing, injecting additional fuel very late in the combustion process, and reducing engine air flow by air system changes such as turbocharger compressor bypass and changing vane settings on variable geometry turbochargers.
What is needed in the art is a system and method of easily increasing the exhaust temperature entering a DOC for effective regeneration of the PF under light loads.